Nonwoven fabrics are conventionally manufactured from webs of staple fibers which are provided, through various bonding techniques, with structural integrity and desired fabric characteristics. Dry-laid techniques in which nonwoven webs are mechanically, chemically and/or thermally bonded are among the most widely utilized processes for manufacturing nonwoven fabrics.
Conventional nonwoven process lines employ carding apparatus to process staple fibers for use in nonwoven fabrics. In the carding process staple fibers are opened, aligned, and formed into a continuous sliver or web free of impurities. An exemplary carding apparatus is illustrated in U.S. Pat. No. 3,768,118 to Ruffo et al.
The art has recognized that fiber orientation within nonwoven web materials employed in dry-laid processes correlates to physical properties in the bonded and processed nonwoven fabrics. Fibers in carded webs are characterized by machine direction ("MD") and cross-direction ("CD") web axes. MD and CD fiber orientations respectively refer to orientation in the process and cross directions on nonwoven process lines. The predominance of MD fiber orientation yields fabrics which have correspondingly enhanced MD and diminished CD tensile strength.
To provide uniform tensile strength characteristics in nonwoven fabrics, the art has introduced techniques which randomize the fibers in the web prior to bonding. For example, it is known in the art to employ airlay systems to randomize carded web materials. Such systems typically include disperser mechanisms which disperse fibers from a mat composed of fibers into a turbulent air stream for randomization and collection on web forming screens. Such apparatus have proved satisfactory in producing randomized web materials, however, this approach requires mechanically complex apparatus which is quite expensive and can be limited in width and speed. Exemplary airlay systems are shown in U.S. Pat. Nos. 3,900,921 to Zafiroglu and 4,089,086 to Contractor et al.
Another approach of the art is shown in U.S. Pat. No. 3,066,358 to H. H. Schiess in which web fiber orientation is modified through adjustment of the angle of interface between a card cylinder and doffing belt in a conventional card. The card cylinder is positioned to rotate in a plane which is angularly offset from the machine direction of the card line and doffing belt to impart cross-directional mechanical movement of the web fibers and enhanced fiber randomization. This approach requires use of complex apparatus and retooling of conventional process lines.
From the foregoing it will be appreciated that the art has long recognized a need to enhance CD tensile strengths in nonwoven webs but has not proposed an entirely satisfactory means of achieving this objective. There is need in the art for an apparatus and process which can be integrated with conventional nonwoven production lines without requirement of extensive and costly retooling.
Accordingly, it is a broad object of the invention to provide an apparatus for enhancing fiber uniformity and CD tensile strength in carded nonwoven webs which is of simple design, can be integrated with conventional nonwoven production lines, and is adaptable to accommodate the different widths and configurations of such conventional nonwoven production lines.
A more specific object of the invention is to provide an apparatus and process for realigning fibers in carded nonwoven webs which obtain improved production line efficiencies and process speeds.
Another object of the invention is to produce carded nonwoven webs having tensile strength characteristics which are improved over the prior art scrambler webs.